In To Kill a Mockingbird, if I was to limit Harper Lee's criticism of Maycomb to two words, I would use "racist" and "classist." Classism, or being a classist, means having a bias based on social or economic position (usually determined in terms of wealth).
I would extend that criticism by saying that Lee is also critical of the cowardice such that people are unwilling to accept social change and being unwilling to change themselves. Part of this is just habitual and how they've been raised. But the other part is a unwillingness that stems not from habit or tradition, but from a desire to keep the status quo, to keep things as they are. A wealthy white family in Maycomb (or any town with strong social traditions) will deny social change (legally and personally) in order to maintain their upper class standing and this must rely on the continued suppression of other people. This suppression, in the context of To Kill a Mockingbird, is both racist and classist. Lee is criticizing this tradition of sustaining racist attitudes (the general fallacious ideology that white citizensshouldoccupy a higher social standing than black citizens) and classist attitudes in order to sustain social and familial traditions (if you're from a poor family, you're going to be poor).
So, Lee is criticizing many aspects of this society and they are individual and sociological criticisms that have to do with racist and classist traditions.